Mixer

ABSTRACT

A batch mixer for continuously mixing multiple batches of discrete material. The mixer comprises multiple mixing chambers which continuously move in an orbital path of movement and while so moving, are filled with material, the material is mixed, and the chambers dumped. Mixing is effected by rotation of a blade mounted within each of the chambers. This invention is an improvement upon the apparatus disclosed and claimed in U.S. Pat. No. 3,319,941, issued May 16, 1967, and assigned to the assignee of this application.

Unite States atet [56] References Cited UNITED STATES PATENTS [72]lnventors Stanley C. Elder;

Albert C. Reckman, Cincinnati, Ohio 810,535

1,011,929 12/1911 Ecaubert.,....1.... 2,482,324 9/1949 Dachkevitch2,984,461 5/1961 Butler. 3,319,941 5/1967 Isaacs...............

Primary Examiner-Robert W. Jenkins Att0rneyWood, Herron and Evans [21Appl. No.

[22] Filed Mar. 26, 1969 145] Patented Feb. 2, 1971 [73] Assignee A. R.Industries, Inc.

Cincinnati, Ohio a corporation of Ohio ABSTRACT: A batch mixer forcontinuously mixing multiple batches of discrete material. The mixer cmixing chambers which continuousl of movement and while so movin [54]MIXER 14 Claims, 9 Drawing Figs.

259/58, material is mixed, and the chambers dum 259/ 174 fected byrotation of a blade mounted ped. Mixing is efwithin each of theprovement upon the apparatus dis- ,319,94l, issued May 16, f thisapplication.

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SHEET 3 OF 3 rsrkr 22 MIXER The mixer upon which this invention is animprovement consists of a continuous mixing apparatus for batch mixingnumerous different types of discrete material. It consists of a frameupon which a generally circular housing is rotatably mounted. Aplurality of mixing chambers are mounted within this rotatable housing.Each of the chambers has an opening in one wall for receiving anddischarging materials as the chambers move continuously past a fillingstation and an unloading station. The mixing chambers are all suspendedfrom rotatably driven shafts which form spokes of the rotatable mixingchamber. Attached to these shafts are mixing blades. These blades rotateas the chambers move through an orbital path of travel.

It has been a primary objective of this invention to provide an improveddrive system for effecting rotary movement of the housing as well asrotational movement of the mixer blades within the chambers.Specifically, it has been an objective of this invention to enable theapparatus to be used to provide a greater range of speeds of rotation ofthe housing and simultaneously to provide a greater range of rates ofrotation of the mixer blades within the chamber.

Another primary objective of this invention has been to pro vide amixing apparatus which is even more versatile and has wider applicationthan the mixer upon which it is an improvement and to accomplish thisobjective while simultaneously reducing the cost of construction of theunit.

These objectives have been accomplished by providing an improved driveto the rotary housing and to the mixer blades. This drive consists of apair of spaced annular rings or bull gears surrounding the housing. Oneof these rings is attached to the housing while the other is freelyrotatable relative to it. Located between and frictionally driven byboth of the rings are a series of rollers attached to the mixer bladesshafts. The two rings or bull gears are independently driven by a pairof variable speed motors such that a differential rate of rotation ofthe rings relative to the housing simultaneously effects rotation of thehousing and of the mixing elements.

With this drive arrangement, a very large range of relative rates ofhousing rotation and of mixer blade rotation may be achieved. The rateof rotation of the mixer blades may easily be increased or decreasedrelative to the rate of rotation of the housing by varying the speed ofone ring relative to the other. Consequently, this drive arrangementprovides a very easily adjusted variable speed mixer which may bereadily set to mix numerous different types of discrete materials.

These and other objectives and advantages of this invention will be morereadily apparent from the following description of the drawings inwhich:

FIG. 1 is a perspective view of the improved mixer of this application;

FIG. 2 is a top plan view, partially broken away, of the mixer of FIG.1;

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 2;

FIG. 4 is an enlarged cross-sectional view of a portion of the machineof FIG. 3;

FIG. 5 is a diagrammatic view showing the relation of thechamber-indexing structure and chamber-inverting means at threesequential positions;

FIG. 6 is a perspective view of a mixing chamber with the mixing bladeremoved;

FIG. 7 is an end view of the mixing chamber showing the blade in itsuppermost position;

FIG. 8 is an end view of the mixing blade with the bucket removed; and

FIG. 9 is a perspective view of a portion of the frame at the dischargestation.

Referring first to FIG. 1, there is illustrated one preferred embodimentof the invention. It comprises a central mixing plant or housing 7 and astationary frame 8 having an elevated cylindrical sidewall 10 with ahorizontal ledge 11 around its upper periphery. As shown in FIGS. 3 and4 the frame includes an elevated circular floor plate 12 attached to thelower periphery of the wall 10 and supported in turn upon dependinglower walls or legs 13, 14. These walls are of a height adequate tosupport the discharge chute 15 of the apparatus at a suitable elevationfor use with trucks, conveyors or the like which are employed to carryaway the mixed materials.

At its center the floor plate is formed with an opening receiving afirst shaft bearing 16. Attached to the plate 12 in surrounding relationto the opening is an upwardly disposed tube 17 having an annular bearingplate 18 at the upper end for supporting a second shaft bearing 19. Aplurality of symmetrically spaced reinforcing webs, two of which areshown at 20, 21, extend radial y from the center tube 17. These webs 20,21 are each rigidly attached to the tube 17, the floor 12, and thecylindrical wall 10, to provide rigidity to the frame and to assist itin supporting the rolling loads of the mixing chambers. The inclinedupper edges 23 of the several webs are located so as to provide a slightclearance with the wall of these mixing chambers as they move around theframe in their upright positions.

Rotatably mounted on top of the frame is a generally circular rotatablehousing 7 having an upper plate 30 containing a plurality of fan-shapedapertures 31 to 36 inclusive, for use in loading the mixing chambers.The plate 30 has rigidly attached thereto a peripheral downwardlyextending wall member 37, herein defined as the outer mixer-shafthanger. The inner surface 9 of the wall member 37 and the undersurfaceof the plate 30 support a plurality of circumferentially spaced,radially extending, reinforcing webs 38 to 43 inclusive (FIG. 2). Attheir inner ends these webs are rigidly affixed to the upper surface ofan annular mounting plate 44. A centering shaft 46 is attached to anddepends from the plate 44. This shaft 46 extends through and isrotatable within the bearing plates 16 and 18 of the frame.

Rigidly attached to the underside of mounting plate 44 is a centralmixer-shaft hanger 47 having a central axial opening 50 for receivingthe drive shaft 46 and radial counterbored sockets 52 for receiving theinner ends of the respective mixer shafts. The housing and its attachedhangers thus form a reinforced bridging element covering the entire topof the stationary frame, and serving as the structure from which theseveral mixing chambers 99 to 99E are suspended.

As best shown in FIG. 3, each of the mixing chambers has a generallytruncated conical shape including a first or outer end wall 60, a secondor inner end wall 61 of smaller size, and an arcuate sidewall 62 havingan aperture 63 of substantial size located therein. A minimum of threeequal-sized mixing chambers is employed, although a greater number isgenerally employed, as, for example, the six equal-sized chambersillustrated herein.

At the axis of the conical shape of each chamber an opening is providedin the respective end walls for receiving a mixer shaft 64. These endwalls have rigidly affixed to the exterior surfaces a pair of aperturedreinforcing blocks 65 and 66 through which the shafts 64 pass. At itsinner end, each shaft is rotatably supported within a socket 52 of thehanger 47 by ball bearing raceways 67. A spacer sleeve 68 maintains theend wall of the chamber a fixed distance from the hanger 47.

A wheel is nonrotatably mounted on the outer end of each mixer shaft 64at a location corresponding to the location of the ledge l 1 of theframe. Each wheel is retained in place by a suitable retainer 76attached to the shaft 64. This wheel 75 rides over and is frictionallysupported upon the top surface of an annular ring or bull gear 82 whichsurrounds the cylindrical wall 10 of the frame. This gear 82 issupported for rotation upon a series of rollers 53 mounted for rotationupon a series of support shafts 54. The shafts 54 are in turn mountedwithin the horizontal ledge or flange 1 l of the frame.

The bull gear 82 is driven in rotation by a pinion gear 80. This piniongear is the output gear of a gear reduction unit which is driven by avariable speed motor 83. The motor 83 is fixedly secured to the frame ofthe machine by a mounting bracket 84.

To prevent the bull gear 82 from moving laterally relative to the frame,a pair of idler gears 88, 89 areengaged with the teeth of the gear 82These idlers 88, 89 are spaced 120 from the drive pinion 80 and arerotatably supported in brackets 90 attached to the frame A secondannular ring or bull gear 85 is supported on top of the rollers 75 andis adapted to be frictionally driven by the rollers 75 This gear 85 isfixedly secured on its inside surface 81 to the vertical depending wall37 of the rotatable housing so that. as explained more fullyhereinafter. rotation of the gear 85 effects rotation of the housing Thegear 85 is driven in rotation by a pinion 86 which is driven from avariable speed motor 87 through a gear reduction unit 91. The motor 87and gear reduction unit are supported from the stationary frame of themachine by a supporting bracket 92 The several wheels 75 to 75D.inclusive. as shown in FIG. 2, serve to support the housing forrotational movement on the bull gear 82. The mixing chambers and theircontents are in turn suspended from the hangers on the lower side of thehousing and the nature of the upper portion of the housing is such thatit acts as a bridge between the wheels located on diametrically oppositesides of the housing to distribute the load on the several wheels.

Referring now to FIGS. to 8. an arrangement is provided for invertingthe mixing chambers seriatim as they pass the discharge station of theapparatus and for restoring them to upright position before they reachan adjacent filling station. This arrangement may take various formswithout departing from the invention, and in the form disclosed hereincomprises a rack 100 serving as a first chamber-inverting means which ismounted upon the upper surface of the ledge 11. This rack 100 cooperateswith pinion gears 101 joumaled for rotation upon each of the mixingshafts 64 of the mixing chambers.

The gears 101 are rigidly fastened, as by removable pins 102, 103 and104, to a weighted chamber-positioning plate 105 to which the side faceof pinion gear 101 is welded. Bolts 107 and 108 join the plate 105 tothe reinforcing block 65 on the end wall 60 of the mixing chamber.

Gear 101, weight 105, reinforcing block 65, and chamber wall 60 are allkeyed to a sleeve 106 rotatably mounted over the shaft 64. Thus rotationof the gear 101 effects rotation of the associated mixing chamberindependently of rotation of the shaft 64 from which the mixing chamberis suspended.

Detachably engaged in the member 105 and projecting forwardly therefromare three chamber-stabilizing pins 109, 110 and 111 having a lengthsufficient to reach beyond the inner periphery of the ledge 11 of theframe during travel of the mixing chambers from the loading station tothe discharge station. Pins 109 and 111, are adapted to slide in contactwith the upper surface of the ledge, and pin 110, which is displacedrearwardly from the leading pin 109, is adapted to slide in contact withthe lower surface of that ledge. As will be understood, rollers or thelike may be employed on these pins to provide a rolling rather than asliding contact, if so desired.

As best seen in FIGS. 2 and 5 an elongated slot 115 is cut from theinner periphery of the ledge 11 adjacent the discharge station of theapparatus. This slot is displaced from the rack 100 in the direction ofmovement of the housing.

Inversion of the mixing chamber and restoration to upright position isillustrated in the diagrams shown in FIG. 5. As the chamber, representedby member 105, is carried to the left by rotation of the housing, thepins 109 and 110 enter the slot 115 when the first tooth of pinion gear101 engages the first tooth of the stationary rack 100. The gear 101then causes the chamber to invert as the pinion gear travels along therack. As seen in the central diagram of FIG. 5, the chamber isupsidedown and its contents are dumped as the chamber passes over theaperture 63 and the discharge chute 15.

As the housing carries the chamber still farther to the left, thechamber is restored to its upright position before the pinion gear 101becomes disengaged from the rack. The pin 109 then comes to rest uponthe upper surface of ledge 11 while the trailing lower pin 1 movesthrough slot 1 15. Rotation of the chamber is then arrested and it is inupright position ready to receive materialat the loading station. As thehousing carries the chamber still farther to the left, pin 111 alsoengages above the ledge 11 and assists pin 110 in preventingcounterrotation of the chamber during loading and during the normalrotation of the mixing blade within the chamber.

5 For the purpose of effecting an efficient mixing of material withinthe chambers during the entire period of travel of the chambers from theloading station to the discharge station, there is provided within eachchamber a hollow sleeve 120 keyed to the shaft 64 as by a key 121 (FIGS.3 and 8). A spiral mixing blade having a leading portion 122 of greatestradius merges into a following intermediate portion 123 of somewhatsmaller radius which in turn merges into still another following portion124 of still smaller radius. Rigid spokes 125, 126 and 127 extendingbetween these portions of the blade and the sleeve serve to hold theblade in proper mixing position with respect to the interior surfaces ofthe chamber. As best shown in FIG. 3, the large leading portion of theblade moves in close proximity to both the end wall 60 of the chamberand the inclined sidewall 62 near the junction with that end wall.During rotation of the blade, it moves material uphill along theinclined wall 62 of the chamber with a tumbling and folding type ofagitation. The material is progressively fed to the intermediate portion123 of the blade and then to the portion 124. During this movement underaction of the rotating mixing blade the material tends to slide down theinclined wall 62 of the chamber under the influence of gravity. Thissliding action preferably is aided by means of a reversely directedblade extension 128 disposed adjacent the end wall 61 of the chamber andhaving a spoke 129 extending to the sleeve.

It has been found that in the mixing of certain materials, the lighterweight and smaller sized particulate matter tends to compact against theend wall 61. By using the blade extension 128, such material ispositively dislodged and returned to the main body of material.Moreover, when the chamber begins its rotation at the start of thedischarge operation, the extension 128 serves to force material towardthe discharge aperture 63 and to clean the chamber region adjacent theend wall 61. The larger portions 122 and 123 of the blade can movethrough aperture 63 during the mixing action.

As may be seen most clearly in FIG. 6, the upper edge of end wall 60 ofthe chamber lies a substantial distance above the axis of shaft 64 sothat splashing of material from the chamber due to blade rotation islargely prevented. The direction of rotation of the shaft 64 ispreferably opposite to the direction of turning of the chamber upon thatshaft when pinion 101 engages with rack 100.

Referring now to FlG. 9, there is illustrated the stationary frame inthe region of the discharge station. It consists of a downwardlyinclined floor plate 132 projecting through an opening 133 in the floorplate 12 of the frame. This inclined plate 132 is fastened at its edgesto the confronting surfaces of the webs 20 and 22 of the frame.Triangular exterior sidewalls 134 and 135 beneath the floor plate 12serve to help define the chute through which material is discharged fromthe apparatus. Material dropping from an inverted chamber is confined bythe webs and 22 and by the inner surface of the circular wall 10 andslides through the opening 133 into the chute. Moreover, when thechamber is inverted at this discharge station the plate 132 is generallyparallel to the adjacent sidewall of that inverted chamber.

OPERATION In operation, the two motors 83 and 87 cause the two bullgears 85 and 82 to be driven in opposite directions. Preferably they aredriven at differing speeds so that they simultaneously effect linear androtational movement of the rollers 75. This rotational movement of therollers 75 about the axes of the shafts 64 causes the mixer blades to berotated while linear movement effects rotation of the chamber supportinghousing. If increased mixing is desired, the two motors, 83, 87 may beset so as to rotate the two gears 85, 82 in opposite directions but atthe same speed with the result that the rollers 75 and attached shafts64 will rotate but will have no linear movement about the axis of theshaft 46. The ratio of rotations of the shaft 64 about its own axisrelative to the rate of rotation of the shaft 64 about the axis of theshaft 46 may be varied by varying the relative rates of rotation of thegears 85, 82 relative to each other. As the relative speeds of the twoapproach the same speed, the shaft 64 will rotate a greater number ofrevolutions per unit of angular arcuate movement of the shaft 64 aboutthe axis 46. As the two speeds are moved further apart so that one isrotating a great deal faster than the other. the number of revolutionsof the shaft 64 per unit of angular movement is decreased, Thus, ifgreater or lesser mixing is desired, this may easily be changed bysimply varying the speed of one orthe other of the two motors.

The primary advantage of this drive assembly is that it provides a widerange of rates of rotation of the housing 7 relative to the frame andthus of the throughput of the complete mixer while simultaneouslyproviding a wide range of rates of rotation of the mixer blades toeffect the mixing of the material in the compartments of the mixer.Additionally, this wide range of throughput speeds and amount of mixingenables a unit to be used for numerous different types of material.Additionally, it is relatively inexpensive to fabricate and manufacture.

These and other objectives and advantages of this invention will bereadily apparent to those persons skilled in the arts to which thisinvention pertains. Therefore, we do not intend to be limited except bythe scope of the appended claims.

We claim: 1. A mixing apparatus comprising: a stationary frame; agenerally circular housing rotatably mounted upon and supported by saidframe, said housing during its movement passing in sequence over adischarge station and beneath a loading station; a plurality ofinvertible mixing chambers mounted within said housing and movabletherewith, each of said chambers having at least one opening in a wallthereof for receiving and for discharging material; means for invertingsaid chambers at said discharge station and for restoring the same toupright position at said loading station; a rotatable element locatedwithin said chambers for effecting mixing of material contained therein,the improvement which comprises: drive means for rotating said housingand for rotating said mixing elements; and

said drive means comprising a pair of rotatably mounted, spaced annularrings surrounding said housing and means interconnecting said rings tosaid housing and to said mixing element so that a differential rate ofrotation of said rings relative to said housing efiects rotation of saidhousing and of said mixing element.

2. The mixing apparatus of claim 1 wherein said annular rings areindependently driven by a pair of variable speed m0 tors.

3. The mixing apparatus of claim 1 wherein said mixing chambers havegenerally truncated conical shapes and are arranged symmetrically withrespect to the axis of rotation of said housing.

4. The mixing apparatus of claim 1 wherein said annular rings arevertically spaced and are rotatable about a vertical axis, the lowermostone of said rings being supported for rotation upon said stationaryframe.

5. A mixing apparatus comprising:

a stationary frame;

a generally circular housing rotatably mounted upon and supported bysaid frame, said housing during its movement passing in sequence over adischarge station and beneath a loading station;

a plurality of mixing chambers mounted within said housing and movabletherewith, each of said chambers having at least one opening in a wallthereof for receiving and for discharging material; I

a rotatable element located within said chambers for effecting mixing ofmaterial contained therein, the improvement which comprises: drive meansfor rotating said housing and for rotating said mixing elements; and

said drive means comprising a pair of rotatably mounted, spaced annularrings surrounding said housing and means interconnecting said rings tosaid housing and to said mixing element so that a differential rate ofrotation of said rings relative to said housing effects rotation of saidhousing and of said mixing element.

6. The mixing apparatus of claim 5 wherein said annular rings areindependently driven by a pair of variable speed motors.

7. A mixing apparatus comprising:

a stationary frame having a generally horizontal circular ledge at anupperportion thereof;

a first rotatable annular ring mounted upon said ledge;

a rotatable housing having an upper bridge portion;

a central mixer-shaft hanger suspended from and supported by said bridgeportion of said housing;

an outer mixer-shaft hanger suspended from said bridge portion of saidhousing adjacent the periphery of said housing;

a plurality of mixing chambers, each chamber having a mixing shaftextending axially therethrough and rotatably supported adjacent itsrespective ends in said hangers, said chambers being symmetricallyarranged about the axis of rotation of said housing and having theirweight supported by the shaft passing therethrough so that the weight ofsaid chambers and their contents is suspended from the bridge portion ofsaid housing;

a wheel rotatably mounted on each of said mixer shafts adjacent theouter ends of said shafts and bearing against said first rotatable ringthereby to support the housing and its attached parts, a second annularrotatable ring surrounding said housing and supported upon said wheels;and

means for rotating said annular rings at a differential rate of rotationso as to effect rotation of said housing and of said mixer shafts.

8. The mixing apparatus of claim 7 wherein said annular rings areindependently driven by a pair of variable speed motors.

9. The mixing apparatus of claim 7 wherein said mixing chambers havegenerally truncated conical shapes and are arranged symmetrically withrespect to the axis of rotation of said housing.

10. The mixing apparatus of claim 7 wherein said housing includesapertures in the upper surface thereof through which apertures materialmay be passed into said chambers while said housing is rotating.

1 l. The mixing apparatus of claim 7 wherein said chambers are supportedfor rotation upon said mixing shafts and including means for invertingsaid chambers at said discharge station and for restoring the same toupright position at said loading station.

12. The mixing apparatus of claim 1 1 wherein the means for invertingsaid chambers comprises a first chamber inverting means mounted on saidframe adjacent a discharge station and asecond chamber-inverting meansrigidly attached to each of said chambers and engageable with said firstchamber-inverting means as said chambers are carried by said housingpast said discharge station.

13. The mixing apparatus of claim 12 wherein said chambers are rotatedthrough one complete revolution by said chamber-inverting means at saiddischarge station and are left with the openings of said chamber in theuppermost position following disengagement of said first and secondchamber-inverting means.

14. The mixing apparatus of claim 12 wherein said first chamberinverting means comprises a rack and said second chamber inverting meanscomprises a pinion gear engageable with said rack.

2. The mixing apparatus of claim 1 wherein said annular rings areindependently driven by a pair of variable speed motors.
 3. The mixingapparatus of claim 1 wherein said mixing chambers have generallytruncated conical shapes and are arranged symmetrically with respect tothe axis of rotation of said housing.
 4. The mixing apparatus of claim 1wherein said annular rings are vertically spaced and are rotatable abouta vertical axis, the lowermost one of said rings being supported forrotation upon said stationary frame.
 5. A mixing apparatus comprising: astationary frame; a generally circular housing rotatably mounted uponand supported by said frame, said housing during its movement passing insequence over a discharge station and beneath a loading station; aplurality of mixing chambers mounted within said housing and movabletherewith, each of said chambers having at least one opening in a wallthereof for receiving and for discharging material; a rotatable elementlocated within said chambers for effecting mixing of material containedtherein, the improvement which comprises: drive means for rotating saidhousing and for rotating said mixing elements; and said drive meanscomprising a pair of rotatably mounted, spaced annular rings surroundingsaid housing and means interconnecting said rings to said housing and tosaid mixing element so that a differential rate of rotation of saidrings relative to said housing effects rotation of said housing and ofsaid mixing element.
 6. The mixing apparatus of claim 5 wherein saidannular rings are independently driven by a pair of variable speedmotors.
 7. A mixing apparatus comprising: a stationary frame having agenerally horizontal circular ledge at an upper portion thereof; a firstrotatable annular ring mounted upon said ledge; a rotatable housinghaving an upper bridge portion; a central mixer-shaft hanger suspendedfrom and supported by said bridge portion of said housing; an outermixer-shaft hanger suspended from said bridge portion of said housingadjacent the periphery of said housing; a plurality of mixing chambers,each chamber having a mixing shaft extending axially therethrough androtatably supported adjacent its respective ends in said hangers, saidchambers being symmetrically arranged about the axis of rotation of saidhousing and having their weight supported by the shaft passingtherethrough so that the weight of said chambers and their contents issuspended from the bridge portion of said housing; a wheel rotatablymounted on each of said mixer shafts adjacent the outer ends of saidshafts and bearing against said first rotatable ring thereby to supportthe housing and its attached parts, a second annular rotatable ringsurrounding said housing and supported upon said wheels; and means forrotating said annular rings at a differential rate of rotation so as toeffect rotation of said housing and of said mixer shafts.
 8. The mixingapparatus of claim 7 wherein said annular rings are independently drivenby a paIr of variable speed motors.
 9. The mixing apparatus of claim 7wherein said mixing chambers have generally truncated conical shapes andare arranged symmetrically with respect to the axis of rotation of saidhousing.
 10. The mixing apparatus of claim 7 wherein said housingincludes apertures in the upper surface thereof through which aperturesmaterial may be passed into said chambers while said housing isrotating.
 11. The mixing apparatus of claim 7 wherein said chambers aresupported for rotation upon said mixing shafts and including means forinverting said chambers at said discharge station and for restoring thesame to upright position at said loading station.
 12. The mixingapparatus of claim 11 wherein the means for inverting said chamberscomprises a first chamber inverting means mounted on said frame adjacenta discharge station and a second chamber-inverting means rigidlyattached to each of said chambers and engageable with said firstchamber-inverting means as said chambers are carried by said housingpast said discharge station.
 13. The mixing apparatus of claim 12wherein said chambers are rotated through one complete revolution bysaid chamber-inverting means at said discharge station and are left withthe openings of said chamber in the uppermost position followingdisengagement of said first and second chamber-inverting means.
 14. Themixing apparatus of claim 12 wherein said first chamber inverting meanscomprises a rack and said second chamber inverting means comprises apinion gear engageable with said rack.